Method and apparatus for resistance welding utilizing application of high pressure

ABSTRACT

A method and apparatus are disclosed herein for electrical resistance welding wherein a high pressure is applied by the welding electrodes to the overlapped portions of metallic blanks concurrently as a high current is supplied to the electrodes.

United States Patent 1 1 1111 3,7 Erlandson Sept. 25, 1973 [54] METHODAND APPARATUS FOR 2,629,806 2/1953 Anderson 219/83 RESISTANCE E NUTILIZING 3,406,272 10/1968 Ehrlich 219/109 1 3,417,221 12/1968 Hayward1 219/109 APPLICATION OF HIGH PRESSURE 3,573,416 4/1971 Drechsler 219/59[75} Inventor: Paul M. Erlandson, Palos Park, 111. 3 1 1OH967 Griswold219/109 I 2,616,014 10/1952 Ellerby 219/109 [73l Assigneez ContinentalCan C0mpany,New

York, NY.

- Primary ExaminerR. F. Staubly 22 F1 d. 24, 1971 l 1 18 Aug AssistantExaminerL. A. Schutzman [21] Appl. No.: 174,378 Attorney-Peterbridge,ONeill & Aubel Related US. Application Data [62] Division of Ser. No.795,515, Jan. 31, 1969, Pat. No.

3,610,862. 57 ABSTRACT [52] Cl 219/64 219/59 1 A method and apparatusare disclosed herein for elc [51 1 l t 823k 1/16 trical resistancewelding wherein a high pressure is up- 58 l 67 109 plied by the weldingelectrodes to the overlapped por- 1 0 can tions of metallic blanksconcurrently as a high current is supplied to the electrodes.

[56] References Cited UNITED STATES PATENTS 5 Claims, 7 Drawing F lgures2,864,933 12/1958 Smith 219/64 ADVANCE FORMING TACK WELD /0 MEANS MEANSMEANS PATENTED SEP251975 SHEET 1 BF 2 r/3 ADVANCE- MEANS if. V

MEANS Ill/ ACTUATOR TACK WELD FORMING MEANS SOURCE OF CURRENT & E D o RC E L E R E D- P U FORGING MEMBER 'razzzzzzzwl -a w:

LOWER ELECTRODE B1 FORGING MEMBER RESISTANCE INCLUDES TOTAL RESISTANCEOF BLANKS AND ALL CONTACT RESISTANCES u m W W w H x x 4 3 2 mEIO OM22wO2 Pm m m JEDEFOM E lo I02 lo ELECTRODE PRESSURE ON BLANK (POUNDS/ so.INCH) PATENTwsEPzsma SHEET 2 0F 2 ACTUATOR FIG. I.

X-RAY GAGE HEAT X-RAY 25 SENSiTIVE GAGE GAGE ACTUATOR -n----- FIG. I.

1 METHOD AND APPARATUS FOR RESISTANCE WELDING UTILIZING APPLICATION OFHIGH PRESSURE This application is a divisional application of copendingapplication METHOD & APPARATUS FOR RESISTANCE WELDING UTILIZING APPLICA-TION OF HIGH PRESSURE, Ser. No. 795,515, filed Jan. 31, 1969 now US Pat.No. 3,610,862, issued Oct. 5, 1971 in the name of Paul M. Erlandson. 1

This invention relates generally toa method and apparatus for electricalresistance welding, and more particularly to a method and apparatus forproviding a seam weld along portions of overlapped metallic blanks.

In the field of welding can bodies, the metallic blanks for forming thecan bodies are commonly formed into a tubular shape having overlappingedge portions which are passed through welding electrodes to weld theedge portions along a seam. Heretofore, the electrical resistance of theoverlapping edge portions has been subject to widev variations and thusthe heat or weld energy generated by the weld current is also subjecttowide variations which tend to produce unsatisfactory welds wheregas-tight'seams are required.

Accordingly, it is a primary object of this invention to provide amethod of resistance welding wherein a high pressure and a high currentare concurrently provided to obtain a minimum variation in theresistance of the overlapped portion and hence effect an improved weld.

Another object of this invention is to provide apparatus capable ofeffecting the method in accordance with the foregoing primary object ofthis invention.

It is another object of this invention toprovide a method of seamwelding can bodies including the forming of blanks into a tubular shapehaving overlapped portions, inserting such portions between two alignedelectrodes which effect a high pressure on said portions and alsoprovide a high welding current to the blanks.

The nature of the invention will be more clearly understood by referenceto the followingdetailed description, the appended claims, and theseveral views illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a diagrammatic'view of a can body seam welding apparatusaccording to the invention;

FIG. 2 is an isometric view of a tubular-cylinder showing theoverlapping portions;

FIG. 3 is an enlarged view, vpartly in cross section, showing a blankbeing welded by the welding electrodes;

FIG. 4 is a graph showing the variation in electrical resistance as afunction of pressure;

FIG. 5 is an end view of the electrodes shaped to enhance lateral flowof the metal;

FIG. 6 is a diagrammatic showing of a portion system of a feedback forcontrolling the applied pressure; and

FIG. 7 is a diagrammatic showing of a second feedback system sensitiveto both temperature, and to lap thickness.

Referring to the drawings, FIG. l-3 indicate in block diagram form anapparatus 10 which may be of any suitable known type for formingmetallic blanks 11 into tubular can bodies. The apparatus 10 includes anelongated metallic horn 12 and advance means 13 for conveying the blanks11 along the born 12. As the blanks 11 are moved along the horn 12,forming means 14 gradually bend the blanks 11 from a flat rectangularshape into a closed cylindrical shape encircling the horn 12 to therebyform the blanks 11 such that the side edges 15 and 16 (see FIGS. 2 and3) meet and overlap to provide a lapped portion 17 of from three to tentimes the thickness of the sheet metal.

As is conventional, the overlapped portions of the blanks 11 are thentack welded by tack weld means 28 at intervals along the length of thelap to hold the edges of the blanks in registration before the blanksare passed through the welding electrodes. The cylindrical tacked bodyblankll is then passed between two juxtapositioned roller electrodes 18and 20 which act both as welding electrodes and as forging members.

Roller electrodes 18 is rotatably mounted and positioned such that theperipheral surface of the electrode 18 contacts the upper surface (asoriented in FIGS. 1 and 2) of the blank edge portion 15 during passageof the formed blank between the electrodes.

The second roller electrode 20 is positioned to be in alignment with thefirst electrode 18 and has its peripheral surface positioned forengagement with a lower surface of the blank edge portion 16 duringpassage of blank 11 between the two electrodes 18 and 20.

' The electrode 20 is rotatably mounted and supported for upwardmovement by a suitable mounting device such as fast acting forceactuator 25 which provides a force to the electrode 20 and the blankspassing between the electrodes.

It will, of course, be understood that while in the embodirnent shownthe electrodes disclosed are of the roller type, the invention is notlimited thereto but is also applicable to apparatus in which other typesof electrodes such as sliding electrodes are utilized.

A suitable current source 35 provides a current of relatively constantamplitude and is electrically connected to the electrodes 18 and 20 bythe conductors or leads 23 and 24 which contact the electrodes 18 and 20through suitable rotary mounting connections 25 and 26. As is known, themetallic horn 12 may, itself, constitute a portion of one of the leads23 or 24 such that conduction of the current occurs through the hornitself or low resistance conductors contained therein.

In accordance with the invention, a high electrode pressure isapplied tothe blank 11 being welded as a high current is concurrently supplied tothe electrodes 18 and 20. Note that the roller electrodes 18 and 20apply a high pressure and a high current to a relatively small area ofthe lapped metal during a given instant. Accordingly, pressures of theorder of 80,000 to 100,000 pounds per square inch, and current densitiesin the order of 5 X 10 amperes per square inch are desirably provided toobtain consistently high quality welds.

As an example, the yield strength of the sheet metal of the blanks 11used in one application is in the range of about 70,00090,000 pounds persquare inch. The electrode force applied is about pounds, and the actualarea of contact between the electrodes and the metal blanks, theso-called electrode footprint," is about 0.040 inches wide and 0.040inches long for an efiective area of l6 X 10 square inches.

At 140 pound force, the equivalent average pressure is about 87,500pounds per square inch. Since the sheet metal is not perfectly smooth,the electrodes initially apply this 140 pound force to a considerablysmaller area consisting of the high points on the sheet metal and,hence, the initial applied pressure is thus very high.

As mentioned above, the relatively high and essentially constant currentis supplied to the electrodes concurrently as the pressure is applied bythe electrodes to the metal blanks 11. The electrical resistance of thesmall area to which the pressure is initially applied is relativelyhigh, and hence the constant current supplied causes this small area tobe heated rapidly. Rapid heating, and hence rapid welding, is requiredsince it is desired to operate the welding apparatus at speeds whereinat least 250 can body blanks, each 5 inches in length, are welded perminute.

The blanks 11 moving in a horizontal plane (as oriented in FIG. 1)provide a force F which has an effective vertical component equal toapproximately 0.1 F. Thus, if the roller electrodes are in a forcedtogether or abutting position, a large horizontal force is required toinsert a blank 11 between the electrodes. Accordingly, it is desirableto program the-force F to vary as a function of time or position of eachblank 11 during the welding cycle. In the embodiment of FIG. 1, a highspeed actuator such as, for example, a Polynoid" actuator is utilized tovary the force exerted on the electrodes.

It has been found that the rate of change of electrical resistancedecreases as pressure is increased in accordance with the curves A and Bof FIG. 4 which curves are representative of the results obtained fromnumerous tests. The resistance indicated in along the axis of theabscissa in FIG. 4 includes the combined electrical load resistances ofthe blank (workpiece) and all the contact resistance present betweenlead 23, electrode 18, blank 11, electrode 20 and lead 24.

Thus, as shown in FIG. 4, the electrical resistance of the blanks 11changes as a function of pressure from a high value at pressures of afew pounds per square inch down to a relatively low and constant valueat pressures of approximately pounds per square inch and above.

Accordingly, when the welding is done under high pressure, changes inelectrode pressures cause relatively minor variations in the resistanceof the electrical load; that is, the resistance presented to the flow ofthe welding current by all the contact resistances in the electricalcircuit as well as the resistances of the electrodes and of the blanksis relatively more constant. Further, at the higher pressures at whichthe apparatus of the invention is operated there is considerably lessdifference between the resistance of the tack weld, and the resistanceof the lap seam between the tack welds thus providing more uniform andconsistent welds throughout the length of the weld seam. The increasedpressure also reduces the arcing and heating at theelectrodes which maybe due to poor electrical contact and thus reduces the wear on theelectrodes as well as tending to produce better, more uniform welds.

Note that the foregoing is in contrast to the prior art which teachesthat relatively light pressure should be exerted on the lapped membersduring heating to increase the electrical resistance offered by theelectrical load, that is, the workpiece. Following this heating phase,some prior art applies a momentary follow-up pressure to forge thematerials together. However, in such prior art processes wherein a lightpressure is applied during heating, the heating process is difficult tocontrol due to the fact that at low pressures a very small variation inpressure will cause a very large variation in load resistance.

The amount of pressure that should be applied to the blanks to be weldeddepends on a number of factors. For instance, while the electricalresistance of the metal increases with an increase in the temperature,the area to which pressure is applied increases as the workpiecesurfaces, as well as the electrode surfaces, are subjected todeformation and, accordingly, the overall electrical resistance betweenthe electrodes and the workpieces as well as the resistance between thetwo workpiece surfaces decreases. Thus, the current density (current perunit area) decreases, causing the heating rate to also decrease. As thesame force is applied to a larger area, the pressure reduces hence theelectrical resistance of the workpiece tends to increase. Thus, sincethere are various unknown variables, it has been found that electrodeforce, and the range of pressures, which should be applied to the blanksto be welded is most conveniently determined by empirical rather thantheoretical means.

Note also that too high of a pressure results in excessive wrinkling ofthe blanks at the laps, and bellying of the can. Further, too highpressures result in excessive wear on the electrodes. Also, as can beobserved from the curves of FIG. 4, a point of diminishing returns isreached wherein the resistance remains essentially constant regardlessof the pressure applied.

The high pressures and the heating of the metal cause a lateral flow ofmaterial such that the thickness of the overlapped areas is reduced byabout 40 percent. That is, if the original thickness of the lap is 2tthe final thickness of the lapped seam is reduced to about 1.2:. In suchmode of operation and within these limits there is little longitudinalflow of the metal, as indicated by the fact that the tack welds are notruptured; nor, is there appreciable buckling or waviness produced alongthe length of the seam.

We have found that with a very narrow lap and very high forging pressurethe normal lapped structure may tend to change to a diagonal interfacetypical of a mashed lap structure. However, with a constant currentpower supply even the sharply reduced lap will not overheat, and thetemperature of the metal at the welding point may actually decrease.This may be due to the fact that when very narrow laps are employedthere is a shearing action between the two pieces which exposesadditional metal to lower the interface resistance and thereby sharplylimit the heating effect of the higher current density. The narrow lapsalso reduce the amount of material added to the circumferentialdimension of thee blank and thus reduces the so-called banana effectand/or ripples or waves.

While lateral flow of the material is obtained by using rollerelectrodeshaving flat peripheral surfaces, lateral flow of the metalmaterial may be enhanced by shaping one of the forging roller electrodesto have a flat contour across the outside of the seam, and the otherforging roller electrode to have a slight radius as shown in anexaggerated showing in FIG. 5. The rapid heating of the metal in the nipof the rollers and the subsequent rapid cooling after passage of themetal from between the rollers tends to inhibit longitudinal flow. Notealso that the electrodes are of much greater width than the lapped blankedges, hence the electrodes contact the entire width of the lapregardless of variations in the position of the lap with respect to theelectrodes.

A feedback control system, as shown in FIG. 6, is provided which sensesthe thickness of the lapped seam emerging from the weldingelectrodes.The sensing unit may comprise an X-ray thickness gage 32, or eddycurrent gage of any suitable type. For any given sheet metal thethickness of the lapped seam emerging from the electrodes is dependenton the pressure applied by the electrodes. The feedback control systemof FIG. 6, thus provides a control to the force being applied to theblanks 11 by the electrodes 18 and 20, in accordance with a preselecteddesired applied pressure. A second feedback control system including aheat sensitive gage 33 of any suitable type may concurrently be employedwhich is sensitive to temperature to provide a control which isdependent on both the heating and forging or pressure applyingfunctions, as shown in FIG. 7.

While this invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention.

'1 claim:

1. Apparatus for forming can bodies through the seam welding together ofoverlapping edge portions of sheet metal blanks comprising cooperatingwelding electrodes,

means for inserting the overlapping edge portions of the blanks betweenand in contact with said electrodes,

electrical conduction means for supplying weld current to saidelectrodes and through said overlapping edge portions,

a current source electrically connected to said electrical conductionmeans for coupling an alternating current to said electrodes to providea high density weld current of approximately 1 X to approximately 5 X 10amperes per square inch to the area of the blank being welded and meansfor applying a force to said electrodes to provide a pressure in theyield strength range of the sheet metal of said blanks on the area tosaid overlapping edge portions in contact with said electrodes wherebythe electrical resistance in said blanks and said circuit 7 is reducedand any variations in electrical resistance is maintained at'a minium tothereby obtain consistently high quality welds, and a feedback controlsystem including means for sensing the thickness of the weld seam andproviding a signal proportional thereto, and means for connecting saidsignal to control the force applied to said electrodes and thereby theeffective pressure. 2. The apparatus of claim 1 wherein said means forsensing the thickness of the weld seam and providing a signalproportional thereto comprises an x-ray thickness gage.

3. The apparatus of claim 1 wherein said means for sensing the thicknessof the weld seam and providing a signal proportional thereto comprisesan eddy current gage.

4. Apparatus for forming can bodies through the seam welding together ofoverlapping edge portions of sheet metal blanks comprising cooperatingwelding electrodes,

means for inserting the overlapping edge portions of the blanks betweenand in contact with said electrodes,

electrical conduction means for supplying weld current to saidelectrodes and through said overlapping edge portions,

a' current source electrically connected to said electrical conductionmeans for coupling an alternating current to said electrodes to providea high density weld current of approximately 1 X 10 to approximately 5 X10 amperes per square inch to the area of the blank being welded andmeans for applying a force to said electrodes to provide a pressure inthe yield strength range of the sheet metal of said blanks on the areato said overlapping edge portions in contact with said electrodeswhereby the electrical resistance in said blanks and said circuit isreduced and any variations in electrical resistance is maintained at aminimum to thereby obtain consistently high quality welds, and

a temperature sensitive system including means for sensing the heatgenerated during the welding of said blanks and providing a signalproportional thereto, and means for connecting said signal to controlthe current supplied to said electrodes.

5. Apparatus for forming can bodies through the seam welding together ofoverlapping edge portions of sheet metal blanks comprising cooperatingwelding electrodes, means for inserting the overlapping edge portions ofthe blanks between and in contact with said electrodes,

electrical conduction means for supplying weld current to saidelectrodes and through said overlapping edge portions,

a current source electrically connected to said electrical conductionmeans for coupling an alternating current to said electrodes to providea high density weld current of approximately 1 X 10 to approximately 5 X10 amperes per square inch to the area of the blank being welded andmeans for applying a force to said electrodes to provide a pressure inthe yield strength range of the sheet metal of said blanks on the areato said overlapping edge portions in contact with said electrodeswhereby the electrical resistance in said blanks and said circuit isreduced and any variations in electrical resistance is maintained at aminimum to thereby obtain consistently high quality welds, and

high speed actuator means for selectively providing a force to saidelectrodes dependent on the position of a blank relative to saidelectrodes.

1. Apparatus for forming can bodies thrOugh the seam welding together ofoverlapping edge portions of sheet metal blanks comprising cooperatingwelding electrodes, means for inserting the overlapping edge portions ofthe blanks between and in contact with said electrodes, electricalconduction means for supplying weld current to said electrodes andthrough said overlapping edge portions, a current source electricallyconnected to said electrical conduction means for coupling analternating current to said electrodes to provide a high density weldcurrent of approximately 1 X 106 to approximately 5 X 106 amperes persquare inch to the area of the blank being welded and means for applyinga force to said electrodes to provide a pressure in the yield strengthrange of the sheet metal of said blanks on the area to said overlappingedge portions in contact with said electrodes whereby the electricalresistance in said blanks and said circuit is reduced and any variationsin electrical resistance is maintained at a minium to thereby obtainconsistently high quality welds, and a feedback control system includingmeans for sensing the thickness of the weld seam and providing a signalproportional thereto, and means for connecting said signal to controlthe force applied to said electrodes and thereby the effective pressure.2. The apparatus of claim 1 wherein said means for sensing the thicknessof the weld seam and providing a signal proportional thereto comprisesan x-ray thickness gage.
 3. The apparatus of claim 1 wherein said meansfor sensing the thickness of the weld seam and providing a signalproportional thereto comprises an eddy current gage.
 4. Apparatus forforming can bodies through the seam welding together of overlapping edgeportions of sheet metal blanks comprising cooperating weldingelectrodes, means for inserting the overlapping edge portions of theblanks between and in contact with said electrodes, electricalconduction means for supplying weld current to said electrodes andthrough said overlapping edge portions, a current source electricallyconnected to said electrical conduction means for coupling analternating current to said electrodes to provide a high density weldcurrent of approximately 1 X 106 to approximately 5 X 106 amperes persquare inch to the area of the blank being welded and means for applyinga force to said electrodes to provide a pressure in the yield strengthrange of the sheet metal of said blanks on the area to said overlappingedge portions in contact with said electrodes whereby the electricalresistance in said blanks and said circuit is reduced and any variationsin electrical resistance is maintained at a minimum to thereby obtainconsistently high quality welds, and a temperature sensitive systemincluding means for sensing the heat generated during the welding ofsaid blanks and providing a signal proportional thereto, and means forconnecting said signal to control the current supplied to saidelectrodes.
 5. Apparatus for forming can bodies through the seam weldingtogether of overlapping edge portions of sheet metal blanks comprisingcooperating welding electrodes, means for inserting the overlapping edgeportions of the blanks between and in contact with said electrodes,electrical conduction means for supplying weld current to saidelectrodes and through said overlapping edge portions, a current sourceelectrically connected to said electrical conduction means for couplingan alternating current to said electrodes to provide a high density weldcurrent of approximately 1 X 106 to approximately 5 X 106 amperes persquare inch to the area of the blank being welded and means for applyinga force to said electrodes to provide a pressure in the yield strengthrange of the sheet metal of said blanks on the area to said overlappingedge portions in contact with said electrodes whereby the electricalrEsistance in said blanks and said circuit is reduced and any variationsin electrical resistance is maintained at a minimum to thereby obtainconsistently high quality welds, and high speed actuator means forselectively providing a force to said electrodes dependent on theposition of a blank relative to said electrodes.